Application of near infrared spectroscopy (NIRS) in the analysis of frying fats

Near infrared spectroscopy (NIRS) in transflection mode using optic probe was applied to determine four analytical criteria values for used deep‐frying fats. Several statistical criteria are used to judge the performance of these NIRS method developments. The results for acid values and for food oil sensor values may be acceptable but the corroborative poorer statistical criteria of calibration for total polar material and dimeric and polymeric triglycerides indicate that both NIRS methods may be considered as adequate only for screening. Further work is required and might be done by additional samples in the calibration sample set.     

Application of ultraviolet spectrophotometry to the analysis of fats and derivatives

Summary There are several spectrophotometric methods available which allow a high degree of accuracy in the analysis of the common fats and oils. Further there are methods available for those fats and oils that contain unsaturated acids up to and including hexaenoic acid which allow good estimations of the composition. Several sources of error are discussed in an effort to point the way to their elimination. Recently published spectrophotometric data on certain polyunsaturated acids isolated from marine oils are discussed in relation to the possibility of extending the method to include these oils. More accurate spectrophotometric constants to be employed in the analysis of certain drying oils are suggested. Presented at the American Oil Chemists' Society, Minneapolis, Minn., October 11–13, 1954. A laboratory of the Eastern Utilization Research Branch, Agricultural Research Service, United States Department of Agriculture.     

Antioxidants and the autoxidation of fats

Summary Experiments on the oxidation of purified methyl oleate support the view that its induction period, and probably that of natural oils, is due to the presence of inhibitors and that purified unsaturated compounds have no induction period, other than the time required for gaseous oxygen to diffuse into the liquid. Experiments with antioxidants indicate that phenolic inhibitors and inhibitols cause no change subsequent to the end of the induction period, that they exert their effect solely by inhibiting the formation of the initial active moloxide, and that they are entirely destroyed before the start of rapid oxidation which characterizes the end of the induction period. The mode of action of several different pro-oxidants is analyzed. Perbenzoic acid, and presumably other peracids, and copper oleate decrease the induction period by virtue of their destruction of natural inhibitors.     

A study of the flavor stability and autoxidation of beef fats

Summary The odoriferous compounds isolated from a fresh edible tallow were found to be very complex in nature and could not be diminished by treatment with carbonyl reagents. When these compounds were removed by deodorization, the bland tallow which was obtained developed on autoxidation another type of odoriferous compounds. The latter contained various carbonyl compounds of the type which have been associated with flavor reversion in edible oils. The characteristic odor of oleo oil and edible tallow could be removed by slight hydrogenation of high selectivity under atmospheric pressure. This hydrogenation process raised the melting point by less than 2°C. but substantially decreased the linolenic and arachiidonic acid content. The hydrogenated products, after deodorization, were not only bland in odor and flavor but also had flavor stabilities better than those of some of the best commercial shortenings. Funds for this study were furnished by a grant-in-aid from Swift and Company, Chicago, Ill. Presented at the American Oil Chemists’ Society meeting, Minneapolis, Minn., October 11–14, 1954.     

Detection and measurement of hydroperoxides by near infrared spectrophotometry

Summary Near-infrared spectra have been measured on a group of hydroperoxides of fatty acid esters and related substances. Only those substances having an −OOH group were found to absorb at 1.46 and 2.07 μ. Dialkyl peroxides and ozonized unsaturated substances had no such maxima in their near infrared spectra although they had high iodometric peroxide values. In a study of the thermal decomposition of methyl oleate hydroperoxide and a study of the autoxidation of methyl linoleate, the intensity of absorption at 1.46 and 2.07 μ paralleled the iodometric peroxide value. This work was aided by grants-in-aid from the Hormel Foundation, the Atomic Energy Commission (Contract AT-11-1-108), the Office of Naval Research (Contract N8 onr66218), the National Live Stock and Meat Board, and the National Diary Council. Hormel Institute Publication No. 170.     

On the kinetics of the autoxidation of fats

The mechanism of fat autoxidation is elucidated from the rate data. All the data treated here and in an earlier publication follow the same basic rate equation, including the time function f(t) empirically derived for heterogeneous oxidation. Metals and glass (the wall of the reaction vessel) are catalysts. Depending on the state of the catalyst, f(t)=t² or f(t)=t. When f(t)=t, the kinetics are first-order as found for monolayer autoxidation, but in bulk phase they are complicated by a transient stage caused by the solubilization of O₂ into the hydroperoxide micelles produced in the exponential (“autocatalytic”) part of the oxidation. Certain additives, such as inhibitors, affect the catalyst and thereby f(t). The kinetics, as determined by O₂ consumption or by analysis of the remaining unreacted substrate, show the first oxidation step. It is unaffected by further chemical changes of the primary oxidation products,e.g., decomposition of hydroperoxides and trimerization in the autoxidation of 9,11-octadecadienoic acid methyl ester.     

Reactions of phosphoric acid in the autoxidation of fats

At the elevated temperatures used in accelerated stability tests phosphoric acid was shown to react with fatty peroxides in such a manner as to prevent their estimation by the usual iodometric methods. A dark, phosphorus-containing precipitate formed, which was apparently polymeric in nature. Phosphoric acid also reacted with oxidized fat to form an undisassociated fat-soluble complex but did not react with fresh unsaturated fatty esters. In addition to the well known sparing action of phosphoric acid ona-tocopherol, it was shown thata-tocopherol and quinone also exerted a marked sparing action on the phosphoric acid.     

Application of high-performance size-exclusion chromatography to study the autoxidation of unsaturated triacylglycerols

A combination of solid-phase extraction (SPE) and high-performance size-exclusion chromatography (HPSEC) was used to study the autoxidation of triacylglycerol (TAG) mixtures separated from low-erucic acid rapeseed oil and butter oil. The samples were autoxidized in the dark at 40°C for four weeks. The polar compounds of the autoxidated samples were separated by SPE (NH₂ stationary phase), and the polar fraction was further characterized by HPSEC with a series of three size-exclusion columns and an evaporative light-scattering detector. The polar fraction contained TAG polymers, polar TAG monomers (PTAG) and diacylglycerols. Peroxide values and anisidine values of the samples were also measured. By using three different types of TAG mixtures, it could be demonstrated that the PTAG content of the TAGs increases during autoxidation. A slight increase was also detected in polymer content. The correlation between PTAG content and the comparative measurements was considered significant. The results indicate that the measurement of PTAG and polymeric material content by HPSEC analysis can be used when studying the autoxidation level of edible oils and in characterizing the autoxidation products of different molecular sizes.     

Applied ultraviolet spectrophotometry of fats and oils

Conclusion The chemist has in the spectrophotometric method a rapid and simple means of studying changes in the double bond systems of fatty acids. The method is highly sensitive. It has found application in studies of processing of oils, improvement of drying oils, catalytic hydrogenation, routine analytical work, soap and tallow control, as well as in nutrition studies in which the composition of depot and ingested fats are of interest. It also finds application in strictly academic studies which have as their purpose an extension of our knowledge concerning the composition of naturally occurring fats and oils. In general, it is especially valuable in cases in which thiocyanometric procedures are not sufficiently sensitive or in which conjugated as well as non-conjugated constituents occur. Presented at the 19th annual fall meeting of the American Oil Chemists' Society, Nov. 7–9, 1945, in Chicago     

Application of wide-line NMR to analysis of cereal products and fats and oils

The principal areas of interest to cereal and oil chemists of wide-line NMR have been reviewed. It provides a rapid method for moisture in cereals where a large number of analyses are required. In the field of plant breeding and genetics of oil seed it provides a non-destructive means of selecting seeds for test and evaluating the seeds grown. In the area of fats, oils and shortenings it provides a rapid and accurate means of measuring the solids content over a wide range of temperatures and can be applied to a finished product as is, under selected conditions. Presented at the AOCS-AACC Joint Meeting, Washington, D.C., April, 1968.     

Antioxidants and the autoxidation of fats IV. Lecithin as an antioxidant

The commercial preparations known as “lecithin” have moderate antixoygenic action on refined cottonseed oil, little effect on lard, and none at all on lard-cod liver oil mixtures. Commercial lecithins contain only small amounts of true lecithin. The antioxygenic agent in these preparations is cephalin. Purified lecithin is not an oxidation inhibitor, but purified cephalin is. There is no quantitative relation between the amount of cephalin used and the prolongation of the induction period. The particular portion of the cephalin molecule responsible for its antioxygenic action is probably the mono-basic phosphoric acid radicle.     

On the kinetics of the autoxidation of fats. II. Monounsaturated substrates

The autoxidation of methyl oleate and oleic acid shows some differences as compared to the autoxidation of linoleate,e.g., the formation of water at an early stage. Linearization of experimental data on the autoxidation to high oxidation degrees of methyl oleate and other monounsaturated substrates shows that the rate equations previously derived for methyl linoleate in the range of 1–25% oxidation are valid, provided the correct expression for the remaining unreacted substrate is used. With monounsaturated substrates, part of the oxygen is consumed by a secondary oxidation reaction almost from the beginning, and only a certain constant fraction α of the total O₂ consumption is consumed in hydroperoxide formation. The fraction α is different for methyl oleate, oleyl alcohol, oleic acid andcis 9-octadecene, but the rate constant for the hydroperoxide formation is the same for all of them when experimental conditions are the same. The main difference between oleate and linoleate autoxidation is the much faster decomposition of the oleate hydroperoxides relative to their slow formation.     

Color tests for the detection of alpha-dicarbon compounds formed in the autoxidation of fats

Summary Tests have been devised for detectingα-dicarbonyl compounds in autoxidized fats. The tests are based upon the conversion of theα-dicarbonyl compounds to their dioximes, formation of the nickelous, cupric and bis-pyridine-ferrous derivatives of the dioximes, and extraction of these colored metallic dioxime derivatives into organic solvent phases. The presence ofα-dicarbonyl compounds in a number of autoxidized fatty materials has been demonstrated by these tests. Peroxides in autoxidized fatty materials could be destroyed by treatment with ferrous chloride without destruction ofα-dicarbonyl compounds. This investigation was aided by the Jonathan Bowman Fund for Cancer Research.     

近红外光谱仪在矿物分析中的应用研究

介绍了利用近红外检测法进行矿物成分分析的原理,并对利用此法的系统硬件和软件进行了描述,说明该法在矿物成分分析中具有实时性、准确性以及成本等方面的优势.     

Kinetics of autoxidation of atactic polypropylene by infrared spectroscopy

The autoxidation of a film of atactic polypropylene was studied by means of infrared spectroscopy. Reaction temperatures varied from 110°C to 135°C and oxygen concentrations, from 5% to 100% by volume. A general reaction scheme previously reported for the autoxidation of polyolefins was utilized for atactic polypropylene. Various results obtained for this polymer were compared with those previously reported for isotactic polypropylene.